1. Technical Field
The present disclosure relates generally to a discharge lamp system, and more particularly to a discharge lamp system controlled by an output voltage of a power factor correction circuit and a controlling method thereof.
2. Description of Related Art
Conventionally, high intensity discharge (HID) lamps have relatively high efficiency, good color rendering, and a long service life, such that HID lamps are widely used in many applications.
Usually, in an HID lamp, a relatively low voltage of 220 V has to be increased to a relatively high voltage rapidly by a ballast, in order to excite a material in a quartz tube for radiating in arc. The high intensity white arc generated by the HID lamp resembles the sunlight during the day. The HID lamp does not have a filament, and therefore, a situation in which a filament is broken to thereby render a lamp inoperable will not occur. In addition, compared to a typical halogen lamp, the HID lamp not only has a longer service life but also has improved penetration, improved illumination and lower power consumption for saving electrical energy. Therefore, the HID lamp has been widely researched and developed with the aim of replacing conventional light sources.
However, when the HID lamp is ignited, the relatively low voltage of 220 V has to be increased rapidly to the relatively high voltage required by the HID lamp. Therefore, the HID lamp cannot be operated alone. That is, a specific power supply circuit is necessary to enable the HID lamp to be ignited and radiate light stably. The conventional power supply circuit for the HID lamp includes a power factor correction (PFC) circuit and an inverter connected to the PFC circuit, where the inverter can be a full-bridge inverter or a half-bridge inverter. The half-bridge inverter has the advantage of relatively low cost, and is therefore frequently selected for use in the HID lamp. However, the HID lamp has a special characteristic. Namely a maximum voltage (i.e., open circuit voltage, OCV) provided to the HID lamp by the half-bridge circuit is only half of the output voltage of the PFC circuit. For example, if the output voltage of the PFC circuit is 400 V, the OCV of the half-bridge circuit is thus 200 V, while the OCV required to ignite the HID lamp is usually in the range of about 250 V to 350 V. Thus, if the typical output voltage of 400 V for the PFC circuit is used in combination with the half-bridge inverter structure, problems will be encountered with respect to the ignition of the HID lamp.